ret

What is ret?

The ret npm package is a library for tokenizing regular expressions. This means it can parse regular expressions into a structured format, making it easier to analyze, manipulate, or transform them programmatically. It's particularly useful for developers working with dynamic or complex regular expressions, offering a way to understand and manipulate the patterns in a more granular and controlled manner.

What are ret's main functionalities?

Tokenization of Regular Expressions

This feature allows you to tokenize a regular expression, breaking it down into its constituent parts. The code sample demonstrates how to tokenize a simple regular expression that matches 'hello' or 'world', case-insensitively. The result is a structured representation of the regex, including its type, sub-expressions, and flags.

const ret = require('ret');
const tokens = ret(/hello|world/i);
console.log(tokens);

Analysis of Character Classes

With ret, you can also analyze character classes within regular expressions. The code sample shows how to tokenize a regex that matches any lowercase letter from 'a' to 'z'. The output will detail the structure of the character class, including its range and any specified characters.

const ret = require('ret');
const tokens = ret(/[a-z]/);
console.log(tokens);

Handling of Quantifiers

This functionality allows for the parsing and understanding of quantifiers within regular expressions. The provided code sample tokenizes a regex that matches between two and four digits. The tokenized output includes detailed information about the quantifier, such as its type and the minimum and maximum number of repetitions.

const ret = require('ret');
const tokens = ret(/\d{2,4}/);
console.log(tokens);

Other packages similar to ret

regexpp

regexpp is a regular expression parser with a focus on providing a detailed abstract syntax tree (AST) for regular expressions. It offers similar functionality to ret in terms of parsing regular expressions but goes further by providing a more comprehensive AST, making it suitable for more complex analysis and manipulation tasks.

regexp-tree

regexp-tree is a toolkit for working with regular expressions in JavaScript. It includes a parser, a regexp transformer, and a regexp compatibility transpiler. Compared to ret, regexp-tree offers a broader range of features, including the ability to transform and optimize regular expressions, making it a more versatile tool for developers.

README

Regular Expression Tokenizer

Tokenizes strings that represent a regular expressions.

Usage

const ret = require('ret');

var tokens = ret(/foo|bar/.source);

tokens will contain the following object

{
  "type": ret.types.ROOT
  "options": [
    [ { "type": ret.types.CHAR, "value", 102 },
      { "type": ret.types.CHAR, "value", 111 },
      { "type": ret.types.CHAR, "value", 111 } ],
    [ { "type": ret.types.CHAR, "value",  98 },
      { "type": ret.types.CHAR, "value",  97 },
      { "type": ret.types.CHAR, "value", 114 } ]
  ]
}

Token Types

ret.types is a collection of the various token types exported by ret.

ROOT

Only used in the root of the regexp. This is needed due to the posibility of the root containing a pipe | character. In that case, the token will have an options key that will be an array of arrays of tokens. If not, it will contain a stack key that is an array of tokens.

{
  "type": ret.types.ROOT,
  "stack": [token1, token2...],
}

{
  "type": ret.types.ROOT,
  "options" [
    [token1, token2...],
    [othertoken1, othertoken2...]
    ...
  ],
}

GROUP

Groups contain tokens that are inside of a parenthesis. If the group begins with ? followed by another character, it's a special type of group. A ':' tells the group not to be remembered when exec is used. '=' means the previous token matches only if followed by this group, and '!' means the previous token matches only if NOT followed.

Like root, it can contain an options key instead of stack if there is a pipe.

{
  "type": ret.types.GROUP,
  "remember" true,
  "followedBy": false,
  "notFollowedBy": false,
  "stack": [token1, token2...],
}

{
  "type": ret.types.GROUP,
  "remember" true,
  "followedBy": false,
  "notFollowedBy": false,
  "options" [
    [token1, token2...],
    [othertoken1, othertoken2...]
    ...
  ],
}

POSITION

\b, \B, ^, and $ specify positions in the regexp.

{
  "type": ret.types.POSITION,
  "value": "^",
}

SET

Contains a key set specifying what tokens are allowed and a key not specifying if the set should be negated. A set can contain other sets, ranges, and characters.

{
  "type": ret.types.SET,
  "set": [token1, token2...],
  "not": false,
}

RANGE

Used in set tokens to specify a character range. from and to are character codes.

{
  "type": ret.types.RANGE,
  "from": 97,
  "to": 122,
}

REPETITION

{
  "type": ret.types.REPETITION,
  "min": 0,
  "max": Infinity,
  "value": token,
}

REFERENCE

References a group token. value is 1-9.

{
  "type": ret.types.REFERENCE,
  "value": 1,
}

CHAR

Represents a single character token. value is the character code. This might seem a bit cluttering instead of concatenating characters together. But since repetition tokens only repeat the last token and not the last clause like the pipe, it's simpler to do it this way.

{
  "type": ret.types.CHAR,
  "value": 123,
}

Errors

ret.js will throw errors if given a string with an invalid regular expression. All possible errors are

• Invalid group. When a group with an immediate ? character is followed by an invalid character. It can only be followed by !, =, or :. Example: /(?_abc)/
• Nothing to repeat. Thrown when a repetitional token is used as the first token in the current clause, as in right in the beginning of the regexp or group, or right after a pipe. Example: /foo|?bar/, /{1,3}foo|bar/, /foo(+bar)/
• Unmatched ). A group was not opened, but was closed. Example: /hello)2u/
• Unterminated group. A group was not closed. Example: /(1(23)4/
• Unterminated character class. A custom character set was not closed. Example: /[abc/

Install

npm install ret

Tests

Tests are written with vows

npm test